1. Field of the Invention
The present invention relates to white balance control apparatus and method preferable for a digital camera and a video camera, which have a solid-state imaging device.
2. Description of the Related Art
In general, a digital camera and a video camera have an automatic white balance control function of automatically correcting a color balance so that the color of a white light source becomes an achromatic color. According to the foregoing function, a chromatic adaptation effect in human vision is falsely added to image data captured. In this way, it is possible to obtain an image having a hue such that something does not feel wrong.
According to a conventional white balance control, there are the following two methods. One is a method of measuring white using an output of a photometric sensor independently from an imaging device of a camera. The other is a method of directly detecting white from image data output from an imaging device.
The foregoing former, that is, the method of using a photometric sensor has the following problems. Specifically, special parts different from a general imaging system are required; for this reason, the cost is high. In addition, an imaging range does not necessarily match with a photometric range due to parallax; for this reason, an error is generated. Therefore, it is general to mainly employ the foregoing latter, that is, the method of directly detecting white from image data output from an imaging device.
If white is detected from captured imaged data, it is general to detect a color close to a black-body radiation locus color as white. In this case, for example, human skin color under daylight and a leaf color of plants under daylight are typically given; in other words, many colors close to a black body radiation locus color exist in a chromatic object color.
For this reason, the color of these chromatic colors is detected as white in error; as a result, correction is made using an erroneous white balance coefficient. Consequently, a problem of lacking the color of the chromatic subject frequently arises.
In order to solve the foregoing problem, the following technique is proposed. According to the technique, an imaging device is provided with a light source area close to a black body radiation locus. Further, skin color and green color areas slightly separating from the foregoing light source area are provided. Moreover, it is determined from the number or the direction of distributions belonging to the foregoing areas whether a target scene is a fluorescent lamp scene or a chromatic color subject scene. Simultaneously, it is determined based on a subject field luminance determined according to an exposure condition in shooting whether the target scene is an outdoor or indoor scene. In this way, it is possible to prevent overcorrection, which is made by detecting a chromatic color subject as a light source in error. (Jpn. Pat. Appln. KOKAI Publication No. 2003-264850)
Moreover, the following technique different from the foregoing technique is disclosed. According to the technique, it is determined from the dispersion of color distribution of the whole of an image whether or not the image is a color chart. In this way, the color chart thus determined is distinguished from a normal scene. (Jpn. Pat. Appln. KOKAI Publication No. H4-371088)